MCI Speedometer

[Sam 4106]

We have an MCI speedometer, with odometer, in our MC8 that has four bolts in the left front brake drum that provide the pulses. This is different from the speedometer shown in the maintenance manual so no help there. Would someone familiar with our speedometer please tell me what the gap should be between the heads of the bolts and the pickup for the speedometer. The gap is about .070" now and I wonder if changing the gap will have any effect on the registered speed. The speedometer registers slow by about 8-10 MPH at 60 MPH on the GPS. Any help will be appreciated.
Sam MC8

[lostagain]

I had to fix the 102D's speedometer a couple years ago. It was eratic and jumpy. I adjusted the gap untill the needle showed a steady speed. I remember that the gap that works is quite a bit wider than what the book shows. I don't think that would have any effect on the speed indicated. Rather, you need to look for an adjustment at the back of the speedo, or if there isnt any, get a smaller or bigger tire.

JC

[bevans6]

I also went with a wider gap.  I used 3/16", maybe a tad more, based on the book recommendation of 1/8th plus minus 1/16th.  The symptom I had was over about 50 mph the speedo would read 50% high, leading the PO to tell me it would run 80 mph all day long with a straight face.  

Now I need to try to figure out how to fine tune it, it reads 10% high.  Which is probably fine, keeps me from getting those pesky speeding tickets...

edit:  rereading your post, i think you are also looking at the fine tuning rather than the it's totally wrong.  maybe we can find out how together...

Brian

[Busted Knuckle]

I've always used a wire brush to make sure there is no flaky rust on the bolts then adjusted them to where a nickle slides between them and the pick up. Always works for me! (sorry never measured the thickness of the nickle!)
  BK 

[bevans6]

My manual includes the instructions that you use a calibrated signal source and and adjust what sounds like a trim pot inside a "pill box" which is a module in the cable up to the speedo, located under the dash on the left hand side.  The trim pot is behind a seal, basically a "break this seal and you own it, warranty just expired" kind of seal    And here I thought my bus was still under factory warranty!  Anyway. minute adjustments to that trimmer with a little screw driver should affect the speedo reading.  The pill box takes pulses and changes them to a voltage output to drive the speedo.  In the absence of a calibration pulse generator, a little trial and error may work fine.

Locate said "pill box", break the seal, attack the trim pot with caution, skill and cunning, you should be on your way to GPS agreement happiness...   If you do this before I do, post back and tell all which way turning the trim pot makes the speedo reading change...

Edit:  Interestingly, I was out in the bus five minutes ago and looking at my speedo, which was changed when my bus was imported to Canada since it needed  to read in KM/hr.  Now, the shift points marked out in different colours were pretty good up to the 3 - 4 shift, which  was way off.  I looked at it and realized for the first  time that it's actually marked for 5 gears, which probably means it's been transplanted from a 5 speed MC-9...   who knew?  Or maybe I have a five speed and I should start trying to shift to the high gear...

Brian

[JackConrad]

Our OEM MC-8 speedometer has an odometer in it. .The speedometer has no adjustment on it. Label on back of the speedometer say "set for 490 Tire RPM" and is made by Dixon. I adjusted the gap between the pick-up and the 4 bolts on the brake drum until it matched my GPS (+- 1-2 MPH). Make sure all 4 bolts are the same distance from the pick-up and free of rust flakes. Jack

[Sam 4106]

Hi Guys,
Thanks for all the info. I'll try your suggestions to see if changing the gap has any effect. I had already wire brushed the heads of the bolts but hadn't driven the bus to see if that made a difference. I'm not sure how to get to the back of the speedometer since there is a custom dash and I haven't figured out how it is put together.
I just got the front air bags reconnected today with the new block off plates so I can drive the bus again. The front of the bus has stayed up at the same height for about 11 hours so I think that was a success. Now to move on to the drive axle and tag to find the air leaks there. I am gradually getting some of the jobs done that the previous owner neglected, along with the new things that develop as we use the bus. I enjoy fixing things, or most things anyway.
Thanks, Sam MC8

[John316]

Sam,

We were told to use a nickel to space the sensor (MCI tech support).

We were having the same issue that you were.

Quick question. Is is consistently to slow? I will give you a tip. When ours did that, we had to get to the back of the speedo. On the back of your speedo there is probably dip switches (to calibrate the odometer) and a screw. The screw calibrates the speedo part of it. You have to drive down the road, and get a helper to turn the screw until the speedo matches your GPS.

If yours is consistently off, I would almost bet that is your problem.

God bless,

John

[Busted Knuckle]

I ain't gonna say that John and others can't be right, and I could be wrong. But I will bet a nickle my trick works, at least it always has for me! (besides I can afford to lose a nickle. If I lose do you want that in cash or check?)
  BK 

[John316]

BK,

It looks like you and I agree on the distance between the sensor and the bolts. Am I missing something? I said to use a nickel, and that is what you said too.

I am simply saying if it is off consistently, we had to adjust our speedo itself. That is a very common thing to have to do. Maybe the PO's hadn't ever adjusted it...who knows.

God bless,

John

[Sam 4106]

Hi Guys,
We took the bus for a ride this morning to test another system and also the speedometer. I wanted to check if wire brushing the bolt heads made a difference. It didn't. The speedometer is still slow by 8-10 MPH at 60 MPH on the GPS so I will have to move on to the back of the speedometer to find the adjusting screw. Just for giggles I measured a nickle and it is .075" thick, so the gap is real close to what BK and John316 said it should be.
Jack, I have 12x22.5 tires and as I recall they are 490 or 495 rev per mile.
Thanks for the help, Sam MC8

[Chopper Scott]

I had better luck using 2 pennies instead of the nickle. I'm not made of money like Bryce and John are!  Just my 2 cents anyway!

[Busted Knuckle]

I had better luck using 2 pennies instead of the nickle. I'm not made of money like Bryce and John are!  Just my 2 cents anyway!

LOL!
  BK 

Scott I'll trade you bills for the month of Aug. (or anytime really but this month is the one I really need help with!) 

[Busted Knuckle]

OH yeah, John I wasn't disagreeing with you. I guess I have just always been lucky and never have had to mess with the adjustment on the speedo itself!
  BK